Ext partition - why so ugly way to have more than 4

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suslik
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Ext partition - why so ugly way to have more than 4

Post by suslik »

I wonder why did Microsoft/IBM introduce Extended partition in MBR to have more than only 4 partitions? I suppose this could be done more easy: 1) reduce code part: 382 bytes are enough and in this case we have 8 partitions descriptors! 2) extend partition table to the next sector: in this case we have 4+32=36 partitions! Yep, not infinite... but more than enough.
Nable
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Re: Ext partition - why so ugly way to have more than 4

Post by Nable »

Almost no-one uses them (because there are better ways of dividing disk space) so why would anyone bother?
Btw, HDDs were ~10-100MiB when people started using MBR scheme, keep it in mind.
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iansjack
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Re: Ext partition - why so ugly way to have more than 4

Post by iansjack »

If it ain't broke then don't fix it.

The current system works just fine. Changing it could break all sorts of things, so why bother?
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Brendan
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Re: Ext partition - why so ugly way to have more than 4

Post by Brendan »

Hi,
iansjack wrote:If it ain't broke then don't fix it.
Problems with the MBR scheme include:
  • A single sector controls everything, and if anything happens to that single sector (e.g. it becomes faulty) you're doomed (no redundancy).
  • No sane/standard way to have more than one bootable partition
  • Partition sizes are limited to 2**32 sectors (2 TiB for 512-byte sectors) and partition start is limited to 2**32 sectors, which limits the size of disks (including large RAID arrays) that can be supported to a max. of 2**33 sectors (4 TiB for 512-byte sectors)
  • The 8-bit "partition type" field wasn't enough (some IDs are used by 2 or more different file systems)
  • No way to give a partition a human readable name, resulting in file systems that include their own "label" and OSs that have to support a file system before they can get the partition's name. Also makes "spare" (deliberately unformatted) partitions unnameable.
  • No way to give a partition a unique ID, so that if a partition is moved (e.g. hard disk replaced) an OS can't find it anymore
For these reasons, MBR partitions was replaced by GPT. Basically, it was broken and was fixed. ;-)


Cheers,

Brendan
For all things; perfection is, and will always remain, impossible to achieve in practice. However; by striving for perfection we create things that are as perfect as practically possible. Let the pursuit of perfection be our guide.
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iansjack
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Re: Ext partition - why so ugly way to have more than 4

Post by iansjack »

I have to disagree. The original MBR scheme is not broken - it works just fine on millions of computers. And it wasn't fixed, or replaced, an alternative was developed. Would you like to take a bet as to which is still the primary method of partitioning a hard disk in a PC?

I've no objection to improved versions being developed, but fixing implies changing the existing version. This would probably break millions of existing installations so is not a good idea.
For these reasons, MBR partitions was replaced by GPT.
Millions of PCs would take issue with that statement.
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